MAZATLAN UNIVALVES 441 



found vary in proportion : the smaller, with 6 normal turns, 

 measuring long. '06, lat. '028. 



The larger ' '087, '033. 



Hob. Mazatlan ; extremely rare, off Spondylus ; ISpool Col. 



Tablet 2026 contains the larger specimen. 



556. LEIOSTBACA PDISTOKTA, var. YOD. 



Melania distorta, Phil. Moll. Sic. vol. i. p. 158, pi. 9, f. 10. 

 Eulima distorta, Desli. in Lam. An. s. Vert. vol. viii. p. 454. 



Phil. lac. cit. vol. ii. p. 135. Forbes fy Hani. Brit. Moll. 



vol. iii. p. 232. Clark, Moll. Test. Mar. JBrit. p. 451. 

 Leiostraca distorta, H, A. Ad. Gen. i. 236. 



L. t. " L. distorta" simillima, sed minima; parte suturali 

 paululum latiore. 



The type of Leiostraca iota, C. 13. Ad. erroneously labelled 

 'Jamaica' in Mus. Cuming, and very incorrectly figured by 

 Sow. is somewhat broader and less bent than the Mazatlan 

 shells : in other respects it exactly accords. After repeated 

 comparison of very fresh specimens with the British dwarf 

 variety of L. distorta, the characters appear exactly alike, 

 except that the sutural portion, which (the shell being tran- 

 sparent) gives an appearance of a spiral line, is slightly nar- 

 rower in the Scarborough specimens received from Mr. Bean. 

 The same glossy deposit over the base, with the rather separate 

 parietal lip, giving in some directions of light the appearance 

 of an umbilicus, appears in each, and of the same shape. Wo 

 difference can be traced in the minute vertex, nor in the varices. 

 The colour in fresh specimens exactly accords. The specimens 

 in Mr. M' Andrew's collection, grouped under Eu. distorta, vary 

 extremely in size and arcuation. The Mazatlan shells are on 

 a much smaller scale, generally more bent, and most beautifully 

 glossy and transparent. The same form occurs in the West 

 Indies (B. M.). According to Deshayes (Lam. An. s. Vert. 

 vol. viii. p. 455, no. 8) it is found fossil in Grignon and other 

 places. If it extends so far back in time, it is natural that the 

 living shell should occupy a widely distributed space. As 

 however the animals may be distinct, both in this and in L. iota, 

 a name is added expressive of its (for the genus) extreme 

 minuteness. The smallest sp. (of 3 normal whirls) measures 

 "035 by '016. A remarkably large sp. measures long. '082, 

 long, spir^ '055, lat. '033, div. 18. 



